This specification relates to polishing pads useful for polishing and planarizing substrates, such as semiconductor substrates or magnetic disks.
Polymeric polishing pads, such as polyurethane, polyamide, polybutadiene and polyolefin polishing pads represent commercially available materials for substrate planarization in the rapidly evolving electronics industry. Electronics industry substrates requiring planarization include silicon wafers, patterned wafers, flat panel displays and magnetic storage disks. In addition to planarization, it is essential that the polishing pad not introduce excessive numbers of defects, such as scratches or other wafer non-uniformities. Furthermore, the continued advancement of the electronics industry is placing greater demands on the planarization and defectivity capabilities of polishing pads.
For example, the production of semiconductors typically involves several chemical mechanical planarization (CMP) processes. In each CMP process, a polishing pad in combination with a polishing solution, such as an abrasive-containing polishing slurry or an abrasive-free reactive liquid, removes excess material in a manner that planarizes or maintains flatness for receipt of a subsequent layer. The stacking of these layers combines in a manner that forms an integrated circuit. The fabrication of these semiconductor devices continues to become more complex due to requirements for devices with higher operating speeds, lower leakage currents and reduced power consumption. In terms of device architecture, this translates to finer feature geometries and increased numbers of metallization levels. These increasingly stringent device design requirements are driving the adoption of smaller and smaller line spacing with a corresponding increase in pattern density. The devices' smaller scale and increased complexity have led to greater demands on CMP consumables, such as polishing pads and polishing solutions. In addition, as integrated circuits' feature sizes decrease, CMP-induced defectivity, such as, scratching becomes a greater issue. Furthermore, integrated circuits' decreasing film thickness requires improvements in defectivity while simultaneously providing acceptable topography to a wafer substrate; these topography requirements demand increasingly stringent planarity, line dishing and small feature array erosion polishing specifications.
For several years, polyurethane polishing pads, such as the IC1000™ polishing pad from Rohm and Haas Electronic Materials CMP Technologies have provided excellent planarization of patterned semiconductor wafers, but the polymeric microballoons are difficult to disperse uniformly and have a broad particle size distribution. These polishing pads have polyurethanes matrices that contain hard and soft segments. Chemically, the soft segments comprise the high molecular weight long chain glycol component of the formulation. Commonly used glycols include polyether glycols (such as polytetramethylene glycol or polypropylene glycol), or polyester glycols (such as poly ethylene adipate glycol). The mobility of molecular chains in the soft segment, which depends on their chemical nature and chain length, results in increased flexibility, toughness and impact resistance. Phase separation increases with increasing chain length and decreasing polarity of the soft segment due to less hard segment/soft segment interaction. Preferred molecular weights are in the 1,000 to 4,000 range. At higher molecular weights, especially at low hard segment amounts, there is a tendency for the soft segments to crystallize that reduces the elastomeric benefits conferred by the soft segments. Soft segments alternate with hard segments that are stiff oliourethane units, principally composed of reacted isocyanate and chain extender moieties. Hard segments act as pseudo cross-links and control the dimensional thermal stability of polyurethanes. Thus, hard segments control properties such as strength and stiffness at elevated temperatures.
The high molecular weight long chain glycols terminate with reactive groups that react with isocyanates to form urethane linkages. Therefore, since the glycols become an integral part of the polyurethane molecular structure and, as such, this limits their ability to phase separate into large discrete domains. Thus, the glycol chains become the connective links between the hard segments rather than existing as well-defined phase domains. As illustrated in the Polyurethane Handbook, 2nd Edition, Edited by Oertel, on page 40, hard and soft domains are intimately mixed at length scales of less than 100 nm. Although these hard and soft domains can provide excellent polishing properties, their scale is too small to impact large-scale-morphology-related properties.
Polyurethane alternative pads, such as polybutadiene pads containing cyclodextrin particles disclosed in U.S. Pat. No. 6,645,264, to Hasegawa et al., have achieved limited commercial applicability. Since Hasegawa et al. introduce the solid cyclodextrin particles by conventional milling techniques, however, it is difficult to achieve a good dispersion having uniform particle size; and agglomeration is a problem.
Huh et al., in U.S. Pat. No. 7,029,747, disclose a polishing pad that includes a liquid mineral phase distributed in a polyurethane matrix. Although the mineral oil is added as a liquid and fairly easy to disperse uniformly, it remains as a liquid phase in the final pad, can leach from the pad during polishing and can contaminate the polished wafer surface.
Shiro et al., in U.S. Pat. No. 6,362,107, disclose polyurethane pads impregnated with acrylate monomers polymerized as a second discrete manufacturing step. The disadvantages of this process is the complex, multi-step sequential manufacturing process involving first polyurethane foam formation, impregnation with an acrylic monomer, followed by subsequent free radical polymerization of the monomer.
There is an ongoing need for improved polishing pads that have superior planarization ability in combination with improved defectivity performance for a variety of electronic applications. Additionally, in order to ensure high wafer throughput, high removal rates and short pad break-in times are required. Furthermore, as semiconductor manufacturing move to increasing temperatures, there is a greater desire for polishing pads with stable polishing performance at high temperatures and over a greater temperature range. Finally, these polishing pads all require manufacturability, pad-to-pad consistency and within pad uniformity.